Slice the cucumbers in half vertically, then slice them into half moons.
Thinly slice the red onion.
Now, it's time to make the vinaigrette, or feel free to make it first and set it aside so it'll already be prepared and ready to pour on the vegetables after being sliced.
Pour the vinaigrette over the vegetables, sprinkle in the parsley, and the crumbled feta cheese. Toss so the vegetables are evenly coated.
Enjoy!
Notes
If you'd like to use a different type of tomato and/or cucumber, feel free to do so.